This application claims priority of European Patent Application No. 99309986.0, which was filed on Dec. 10, 1999.
1. Field of the Invention
This invention relates to a mobile radio telecommunications system, such as a Universal Mobile Telephone System or the Global System for Mobile Communications, and relates especially to a system providing real time services.
2. Description of the Related Art
In a real time service, it is important that uplink packets, that is packets passing to a mobile system from the control network, are neither duplicated nor lost. If a packet is duplicated, then the upper control layers must deduce which packet to discard; if a packet is lost, it must be retransmitted and if retransmission is imperative, this is usually carried out in the application layer and the retransmission requires radio resource.
Some real time services, such as video, are delay-sensitive and/or loss sensitive. Packet loss and packet duplication can seriously affect the ability to provide such services. Packet loss and packet duplication are especially likely to be experienced during a handover or relocation from one control network to another as the mobile user moves on the ground.
In this specification, the terms xe2x80x9chandoverxe2x80x9d and xe2x80x9crelocationxe2x80x9d, which mean the transfer of control of a connection from a serving Radio Network Controller (RNC) to a target RNC, are used interchangeably.
In a mobile radio telecommunications system it is at present not possible to avoid packet loss or packet duplication during handover or relocation.
It is an object of the invention to provide a system in which the risk of packet loss or packet duplication during handover is substantially reduced.
According to the invention in a mobile radio telecommunications system, a method of handing over control of a mobile from a serving controller to a target controller, characterized by the steps of:
the target controller sending to the serving controller a request for timing information;
the serving controller sending timing information to the target controller;
the target controller coming into user plane synchronization with the serving controller for this mobile connection;
and the target controller taking control of the mobile.
Preferably the timing information is frame timing information.
Also according to the invention, a controller for a mobile radio telecommunications system arranged, on handover of control of a mobile to that controller, to send a request for timing information to a serving controller; to receive timing information from the serving controller; to come into user plane synchronization with the serving controller for this mobile connection; and to take control of the mobile; and further arranged, on handover of control from that controller to a target controller and on receipt of a request signal, to send to that target controller signal timing information.